Mildew-proofing of leather



June 10, 1958 s. DAHL ETAL 2,338,426

MILDEW-PROOFING OF LEATHER Filed Feb. 18, 1957 2 Sheets-Sheet 1 SPORE GROWTH ON LSAMPLELS- OF DIFFERENT 5A MPLES 0F LEATHER TESTED UNDER FOLLOWING CONDITIONS."

SAMPLE I SAMPLE 11 5A MPLEm SAMPLE 12 EXPOSED T0 EXPOSED TO NOT EXPOSED EXPOSED TO WEATHE- WEATHERING WEATHER/N6 To WEATHER m PANAMA JUNGLE FUNGICIDE AT VUMA IN WA5H,D.C I m IXXXZOIP 1 or P 10 P 4-NITROPHENOL A R A q L,

- I0J5L'J. LL -JLL gnu L {CK 3 B) S(4NITROPHENYL) %60Q I I I I7 I I I I Q Q CARBONATE 10.1 C? O C OK 3/5 (2'CIIIL0E0-4 NOT NOT L E SAMPLE TESTED NITROPHEN YL.) TESTED TESTED 5 O VE6. soLE LEATHER CARBONATE I CRUST.

060 f C 4-N1TR0PHEN0L I050 I I I I I I I I I O Q lals L J] S O B BIAS-(4-NITROPHENYL% I I I I I I I L CARBONATE mm IUII JL 8 I Bl-5(2-CHLOR04- I LEATHER r r I 4-NITROPHENOL U *0 0 "0 00 I015 T V OO 6 BIS-(4-NITR0PHENYLM6O I I I 0| l E Q C CARBON TB ii if; I I BIS (2-CHLOR0-4- 1 SAMPLE TESTED r y NOT T I MILITARY TYPE CQRBONATE I TESTED TESTED UPPER LEATHER N0 FUNGCIDE v v v v. E. v I ..V E. v v

(CONTROLS) 5.0.0.0000. 0..0. 0 0.0.0. 00.0.0.0. L..- 4. 1

EXPOSURETIME, WEEKS- I 234567 T254567 1254567 I 23456 789101112 LEEEND INDEX 1 I N0 MILDEW LJ; :-25% OF SURFACE AREA MILDEWED INVENTORS 1 I 26'50/ 0F suRFAcE AREA MILDEWED 5:45 /2 0F suRFAcE AREA MILDEWED S Dahl 76-l00/o OF SURFACE AREA MILDEWED I A p BY M x 5;; ATTORNEY A'EENT June 1958 s. DAHL ETAL 2,838,426

MILDEW-PROOFING OF LEATHER Filed Feb. 18, 1957 2 Sheets-Sheet 2 SUMMARY OF ACCUMULATED M/LDEW GROWTH 0N VARIOUS SAMPLES 0F LEA THEE TESTED NDER F/ELD TEST COND/T/OMS LISTED IN F7611 SAMPLEI SAMPLEIT SAMPLEflT SAMPLEDZ LEATHER LEAn/ER LEATHER LEATHER FUN/CIDE L J v Q Agjc A E? A-(M 4-N/TROPHENOL B 4 L B B I B XL) 6 I) 6 [11?) C J) C L 1Q m \f \f A BIS-(4-N/TR0PHENYLjv 2 g A g YA C c 1 c J j c \J It 51512 -cAL0 0-4- N/TROPHENYL) CARBON/17E c u FUNG/C/DE IN LEATHER, 15.30am 153050 153050120 ..l5.30.60

LEGEND LEATAER N0 M/LDEW A =1/EEETABLE SOLE CRUST /-25% oFsuREAcE AREA M/LDEWED IB= VEGETABLE STRAP m 26-50% 0F suRFA CE AREA M/LDEWED c MIL/T4 TYPE UPPER I. I 51-75% OFSUAFACE' AREA M/LDEWED (CHROME R574 1 I 764007; 0F JURFACE AREA MILDEWD AGE/VT 2,838,426 MILDEW-PROOFING F LEATHER Sverre Dahl, West Hyattsville, Md., and Arthur Milton Kaplan, Waban, Mass., assignors to the United States of America as represented by the Secretary of Commerce Application February 18, 1957, Serial No. 640,993 3 Claims. (or. 117-142 This invention relates to the fungus-proofing of leather and particularly contemplates an improved process for rendering leather mildew resistant in hot and humid areas.

Most tanning agents and leather lubricants employed by the production of satisfactory leathers, particularly for military use, are mildew susceptible. This is particularly true of vegetable-tanned leathers. It is, therefore, necessary to incorporate suitable fungicides into the leather to inhibit mildewing. Present practice as employed by the Quartermaster Corps of the United States Army, for example, employs 4-nitrophenol as a fungicide. A comprehensive review on the use. of such compound as aleather fungicide is presented in an article by R. M. Lollar, J. Am. Leather Chem; Assn. 49, 605 ,(1954).

To avoid the possibility of material shortages, particu larly in times of national emergency, the present invention offers a substitute fungicide which is comparable in effectiveness to 4-nitrophenol in inhibiting mildew growth. Moreover, since 4-nitrophenol is colored, the present invention has the further advantage of not adversely affecting the appearance of the leather treated with the fungicide. In addition, the compound of the present invention is reported to be considerably less toxic than 4-nitrophenol. j

Accordingly, the objectives of the present invention are to provide an effective fungicidal treatment process for leathers to prevent mildew growth which is nontoxic and which will not adversely aifect the appearance of the leather.

' Other uses and advantages of the invention will become apparent upon reference to the specification which:

Fig. l is a chart showing weekly observations on relative mildew growth on fungicidal-treated leather samples when subjected to different environmental conditions, and

Fig, 2 is a mildew-growth chart summarizing the effectiveness of various fungicides tested as indicated in Fig. 1. It is generally recognized that the fungitoxicity exhibited by a given compound against a specific organism is greatly influenced by the substrate and by other environmental factors. Leather is a complex material that supports the growth of a great'variety of organisms, most ofwhich have been studied to only a limited extent. For example, compounds which are found to be effective fungicides for other materials, such' as textiles or paints, or which exhibit fungicidal activity in tests using pure cultures and nutrient agar medium are not necessarily good leather fungicides. From these considerations it is-obviously desirable to evaluate leather fungicides on a leather substrate and preferably under the conditions and against microflora typical of those existing in a tropical jungle.

In orderjto accurately evaluate the effectiveness of the fungicides comprising the present invention the mildewproofing properties thereof were determined on the basis a of a comparison with the mildew properties of 4-nitrophenol employed as a control. On the basis of such tests it was determined in accordance with the principles is of this invention, that treating leathers with compounds comprising bis-(4-nitrophenyl)-carbonate and bis-(2-chloro-4-nitrophenyl)-carbonate constitute an effective fungicide treatment for mildewproofing of leather. The exact procedures for treating and testing the leather in accordance with the present invention and the experimental procedures for determining the fungitoxic properties thereof is detailed in the ensuing description.

Incorporation of fungicides into the leather Leather specimens were dipped into a suitable organic solvent-type formulation of the fungicide. As has been 1 previously determined, the choice of solvents apparently does not affect the fungitoxic properties of the compound. See also A. J. Musgrave et al., J. Soc. Leather Trades Chemists 35, 290 (1951). a

Both preliminary laboratory type, and field tests were employed to evaluate the efiicacy of the mildewproofing treatment comprising the present invention. The preliminary or initial tests were performed in accordance with the following detailed procedures.

Tests of mildew resistance Preliminary test The fungicides were tested as follows: The fungicide was dissolved in an organic solvent as above indicated.

The solution was then applied to 2- by 4-inch vegetabletanned sole leather specimens by immersing the leather in the solution. The pickup of fungicide was determined by differences in weight before and after immersion. The speciments were dried for a minimum of 24 hours and cut into four specimens 1 inch by 2 inches.

Testing was done according to Federal Specification KK-L-3l1a, Leather; Methods of Sampling and Testing, Methods 5011 and 5021, as follows: Mycelial mats were prepared by suspending the spores of a ripe, fruiting agar culture of Aspergillus niger (ATCC6275) in 100 ml. of distilled water containing a, small amount of wetting agent. Using a sterile camels hair brush, the spore suspension was brushed uniformly over the surface of a hardened, sterile nutrient agar medium. Prior to inoculation, the culture medium was sterilized in an autoclave of 20 minutes at 122 C., poured into sterile 3-inch Petri dishes under aseptic conditions, and allowed to harden. After inoculation, the Petri dishes were incubated for approximately 48 hours at 29? C., relative humidity 90 percent. At the end of the incubation period, the surface of the agar medium was covered with a white mycelian mat of the test organism. Two of the 1- by 2-inch leather specimens were tumbled for three hours in shake bottles containing distilled water. These specimens plus a third nontumbled specimen were placed on the mycelial mats of A. niger.

Thespecimens were incubated for 7 days at 29 C. at a relative humidity of 85 to 90, percent. A leather specimen free of fungicides was exposed concurrently as a control. I If the control failed to show a heavy growthof mildew the test was repeated. The results of the tests were determined by visual examination of the specimens.

Other specimens were tested for resistance to mildew growth by the American Leather Chemists. Association sand spore mixture. 21 days under the same conditions described previously. Visual examination for mildew growth was made on the 7th, 14th, and 21st 'day of the incubation period.

The fungicides were then tested further by a tropical room exposure test. The facilities of a tropical room located at the Engineering Center, Fort Belvoir, Virginia, were employed. Such room provided conditions including flora typical of a tropical jungle. Leather specimens containing 'definite percentages of the fungicides were exposed for five weeks in the tropical room. The spec iv Patented June 10, 1958 I These specimens were incubated for 3 mens were inspected for mildew growth once each week.

The minimum percentage of a given fungicide required to make the test leather mildew resistant in the tropical room exposure test is assumed to be the percentage required for protection under the most servere conditions military leather items will encounter during service. As a control, 4-nitrophenol present in the leather at 0.3 percent concentration, prevents mildew growth under the tropical room conditions. Generally, no higher concentration than 0.6 percent has been used.

If a compound does not exhibit at least some inhibition of mildew growth at 0.6 percent, it is considered too ineffective to be of value. Others are unsuitable as leather fungicides because of obvious defects from the standpoint of color, stability, and solubility characteristics, or possess properties considered harmful to human health. Consequently, the components of the present invention can be considered as substitutes or alternates for 4-nitrophenol as a leather fungicide.

Field exposure tests SCREENING TEST RESULTS (TROPICAL ROOM) OF FUNGICIDES USED IN FIELD EXPOSURE STUDY Borderline concentration,

Name Percent, Minimum amount required 4-nitrophenol (comparison standard) 0.30 bis(i-nitrophenyl) carbonate 0.30 bis(2-chloi'o-4-nitropl\euyl) carbonate 0.30

Preparation of leather samples for field tests A-Vegetable-tanned sole leather crust. B-Vcgetable-tanned strap leather. C-Chrome-retanned military-type upper leather.

All of these leathers were obtained free of 4-nitrophenol or any other fungicide. Four bends of leather A, four sides (half hides) of leather B, and two hides of leather C were used. Four like sets of leather samples were prep red, one each for the four exposure sites used. Each of the fungicides was tested at three concentration levels, and three specimens of each type leather were used for each level. In addition, three controls (specimens containing no fungicide) of each type leather were included in each set of samples. The size of each specimen was 2 by 4 inches. Only those portions of the bends, sides, or hides that were free from obvious flaws, such as scars and creases, were used. All specimens of each leather were cut out, mixed, and assigned to fungicide treatments and to sets of samples at random, and marked for identification.

Formulations T he prcviously-rcferred-to vehicle for incorporating the fungicide in the leather was prepared as follows. A 5- percent (by weight) organic solvent stock formulation of each fungicide was first prepared. Portions of the stock formulation were then diluted to the concentrations required to deposit the desired percentage of fungicide in the leather (0.3-0.6 percent by weight of dry leather). All dilutions of the stock formulation of a given fungicide 4 Were made with the same solvent mixture as was used in that stock formulation.

The specific formulation compositions employed were as follows: For bis(4-nitrophenyl) carbonate and bis(2- chloro-4-nitrophenyl) carbonate 50 percent dioxane, 10 percent neats-foot oil, and chloroform to make to 100 percent.

Concentration levels of the fungicides in the leather As has been mentioned, each fungicide was tested at three levels of concentration based on the approximate borderline concentration indicated in Table I above. The three levels were: Highest Level: twice the borderline concentration 0.60% Intermediate Level: borderline concentration 0.30%; Lowest Level: one-half the borderline concentration 0.15%.

Treatment of leather specimens The leather specimens were treated by dipping into formulations of the required concentrations to give the desired percent depositions of the fungicides in the leather. The required formulation concentrations were calculated from the average percent of the formulation absorbed by the respective leathers during the treatment, determined in preliminary experiments. The calculated percent depositions of the fungicides in the leathers were checked by analyses in the case of 4-nitrophenol by method 6711 of Federal Specification KKL-3lla Amendment -l, June- 17, 1953. The agreement between the calculated fungicidepercentages and those found by analyses was of the order that could be expected from the variability in formulation absorption by individual specimens. This variability is shown in the following table.

TABLE II Formulation absorption Number of Leather specimens tested Average, Range,

Percent Percent All specimens of one leather receiving the same treatment were treated simultaneously. The controls (specimens'containing no fungicide) were treated with a solution comprising only the inactive solvent component used in the fungicide formulations. After treatment, the specimens were placed in an oven at C. for 6 hours in order to remove the volatile solvents.

Exposure conditions Four like sets of leather samples, prepared and treated as described, were exposed as follows:

Sample Set I.Exposed at Yuma, Arizona (desert weathering, hot-dry environment). The samples were exposed to direct sunlight but were sheltered from desert storms. They were reversed twice during the exposure period so that grain and flesh surfaces received about equal amounts of sunlight. The exposure lasted for three months and the samples were subsequently tested for mildew resistance by storage in the tropical room at Fort Belvoir, Virginia, as previously described.

Sam le Set II.Exposed on a roof at the National Bureau of Standards, Washington, D; C. (weathering, moderate hot-dry environment). The samples were exposed in the open during working hours, but sheltered the rest of the time and during rainstorms. Grain and flesh surfaces received about equal sunlight exposure. The exposure period and subsequent mildew-resistance test were the same as described forSample Set I.

Sample Set lII.-Not exposed to weathering. The samples werestored in the laboratory and were not exposed to any direct weathering before they were tested for mildew resistance by exposure in the tropical room.

Sample Set I V.Exposed in Panama (mildew-growing conditions, hot-humid environment). The samples were protected from direct sunlight and rain, but were otherwise exposed to an ambient environment at a site located in the jungle on the Atlantic side of the Isthmus of Panama. Weekly observations of mildew growth on these samples were made for a period of 12 weeks (from August 1 to October) after growth began toappear on some specimens. Previous to this period, the samples had been exposed at two other Panama sites for a total of five weeks, during which time no mildew growth appeared even on untreated specimens. The environmental conditions at the first two sites apparently were unsuitable for.

rapid mildew growth and made relocation necessary.

It may be observed that none of the exposure conditions was' such that specific information about the effect of leaching by water on the permanency of the fungicidal treatments could be obtained. However, both in the Panama exposure and in the tropical room exposure the samples were wetted to the point of dripping during repeated condensations of the humid atmospheres. Some leaching efiect, is therefore, considered to be included in the'over-all efiectiveness of the fungicides under these conditions.

Weekly observations on mildew growth were made and recorded separately for the grain and flesh areas and the edges of each specimen. The amount of mildew growth was indicated by the percentage of the given area covered with it and was designated by the following code numbers:

-No mildew growth.

1From scattered colonies to 25 percent of the area covered with mildew growth.

2Fr0m 26 percent to 50 percent of the area covered with mildew growth.

3From 51 percent to 75 percent of the area covered with mildew growth.

4-From 76 percent to 100 percent of the area covered with mildew growth.

The treatment of the original test data to obtain the data shown in Figs. 1 and 2 was performed as follows:

(a) Derivation of a single value for each specimen If the values recorded for grain and flesh on a given specimen were the same, that value was taken as the value for the specimen. If they were not the same, the higher value was taken as the specimen value rather than the average. It is assumed that mildew growth is equally objectionable whether it grows on grain or flesh. If a fungicide does not give the same protection to both sides of the leather, it should be rated according to the area on which it is least effective.

Mildew growth on the edges was neglected. The sizes of edge areas are negligible compared to grain or flesh areas. Furthermore, the cut and loose fibers of edge areas are not typical of the surfaces that are of most concern in leather mildew prevention.

(b) Derivation of a single value for each treatment After a single value for each of the three specimens receiving the same treatment was obtained as explained under the four conditions defined by the vertical columns designated Sample I, Sample II, Sample III, and Sample IV. The darkened areas in the circles are a visual representation of the mildew growth, the relative effect of which-is indicated by the legend index at the bottom of Fig. 1. Fig. 1D indicates typical mildew growths on leather specimens containing no mildew proofing for purposes of comparison. Weekly accumulations of mildew growth on leathers containing the various concentrations of each of the three fungicides are shown. The tropical room exposure was terminated after five weeks. The Panama exposure was terminated after 12 weeks at the final exposure site. Fig. 2 is a compilation of information, taken from Fig. 1, showing the final accumulations of mildew growth on all leathers of the various sets of samples after completion of the mildew-resistance tests.

The samples labeled as I, II, III, and IV in the vertical columns, Fig. 1, represents the following enumerated conditions of test:

Sample Set I was exposed to weathering at Yuma, Arizona.

Sample Set II was exposed to weathering on NBS roof.

Sample Set III was not exposed'to weathering (store in NBS lab).

These samples were then tested for mildew resistance by exposure in the tropical room previously referred to.

Sample Set IV was not exposed to weathering prior to being tested for mildew resistance by exposure at a Panama jungle site.

Tropical room exposure'versus Panama exposuredew growth generally appeared on'corresponding specimens after shorter exposure times in the tropical room than at the Panama site (Fig. 1). This is to be expected since the tropical room is controlled so as to produce continuous optimum conditions for mildew growth, while at the Panama site natural atmospheric conditions prevailed. The latter conditions were not uniformly optimum for mildew growth. Figure 2 shows that the two sets of samples yielded final data that are in good agreement. However, there are clear indications that a 5-week exposure period in the tropical room is at least as severe a test for mildew resistance as a 12-week exposure period at the Panama jungle site.

Efiect of weathering Comparison of the three sets of samples exposed to mildew growth in the tropical room, but previously exposed to different weathering conditions'(Sample Sets I,

II, and III), shows that weathering appears to make theleathers slightly more susceptible to mildew growth. This diiference is persistently reflected in the final data also, as may be observed from Fig. 2. The greater mildew susceptibility of weathered samples may be due to greater accumulation of dirt and spores on them compared to samples that were stored in the laboratory. It may also be due to fungicide removal or degradation caused by weathering.

The results of this study show no appreciable differences among the fungicides in sensitivity to weathering.

. There is no appreciable difference in mildew resistance between the samples exposed to weathering at Yuma, Arizona, and those exposed on a roof at the National Bureau of Standards, Washington, D. C.

Relative eflectiveness of the fungicides used 7 Conclusions It was found that bis(4-nitrophenyl) carbonate and bis(2-chloro-4-nitrophenyl) carbonate prevent mildew growth on leathers under tropical jungle conditions at concentrations of from 0.30 to 0.60 percent and are adequately stable under severe weathering conditions.

Compared to the eflectiveness of 4-nitrophenol, the bis(4-nitrophenyl) carbonates are only slightly less effective, considering the over-all results of this study.

What is claimed is:

l. A substantially mildew-proof leather containing from 0.3 to 0.6 percent by weight of dry leather of bis(4-nitrophenyl) carbonate.

2. A substantially mildew-proof leather containing about 0.6 percent by weight of dry leather of bis(4-nitrophenyl) carbonate.

3. The process of rendering leather mildewproof comprising the steps of making a solution comprising approximately 5 percent of bis(4-nitrophenyl) carbonate, 50 percent di-oxane, 10 percent neats-foot oil and 35 percent chloroform, diluting the solutions to provide a concentration of said bis(4-nitrophenyl) carbonate of from 0.3 to 0.6 percent by weight of dry leather, impregnating the leather by immersing in the diluted solution until the desired concentration of said carbonate is obtained and drying said impregnated leather.

References Cited in the file of this patent UNITED STATES PATENTS Virtanen Jan. 26, 1937 OTHER REFERENCES 

3. THE PROCESS OF RENDERING LEATHER MILDEW PROOF COMPRISING THE STEPS OF MAKING A SOLUTION COMPRISING APPROXMATELY 5 PERENT OF BIS(4NITROPHENYL) CARBONATE, 50 PERCENT DIOXANE, 10 PERCENT NEAT''S-FOOT OIL AND 35 PERCENT CHLOROFORM, DILUTING THE SOLUTIONS TO PROVIDE A CONCENTRATION OF SAID BIS(4-NITROPHENYL) CARBONATE OF FROM 0.3 TO 0.6 PERCENT BY WEIGHT OF DRY LEATHER, IMPREGNATING THE LEATHER BY IMMERSING IN THE DILUTED SOLUTION UNTIL THE DESIRED CONCENTRATION OF SAID CARBONATE IS OBTAINED AND DRYING SAID IMPREGNATED LEATHER. 